The present invention generally relates to devices for weighing an object. The invention specifically relates to an improved overhead track scale.
Overhead track scales have been used in various industries. In the meat industry such scales have been used to weigh beef or pork carcasses for example. Such scales in the past have been suspended from an overhead lever system. In use, the object to be weighed is suspended by a steelyard rod from a scale having a mechanical weighing system with an indicating dial.
In the late 1960's and early 1970's the mechanical weighing system was replaced with an electronic device. In this type of system, a load cell was placed in the steelyard rod and connected to a digital indicator. The weight of the load placed on the steelyard rod was electronically displayed on the digital indicator. In the latter 1970's, the steelyard rod was replaced with a live rail which was hung from tension load cells. The live rail was checked from moving sidewards by steel rods. The steel rods were mounted between the live rail and an adjacent structure.
Track scales also have been used in the railroad industry to measure the weight of railroad cars. Such track scales have used load cells to support a live rail. The load cells have been shear beam load cells which create a signal proportional to the load applied to the load cell. Such have been constructed and operate on the principal that shear beam load cells are not sensitive to a change in the location of the loading point along the length of the shear beam load cells.
However, it is known that, if a variation in the location of the loading point along the length of a shear beam load cells occurs, some change in the indication of the weight measured by the shear beam load cell will occur. Specifically, it is known that approximately a 0.05% change in the weight measured by a shear beam load cell results from approximately a 1/8" change in the location of the loading point along the length of the shear beam load cell. Accordingly it is desirable that the loading point of a shear beam load cell remain fixed along the axial length of the load cell in order to obtain accurate weight measurements.
Also, railroad weighing devices which utilize shear beam load cells for supporting a live rail have been constructed so that the weighing devices can be readily installed in existing systems. Specifically, the construction of the weighing device is such that the installation may be made even though there is some misalignment of certain parts of the system such as the approach rails on opposite ends of the live rail. Typical embodiments of such weighing devices are shown in U.S. Pat. Nos. 3,734,217 and 3,714,997. The weighing devices shown in these patents are constructed so that certain misalignment of parts is compensated for in the installation of the weighing device. Obviously, the advantages of such systems would be desirable in a track scale where the load is applied at the same axial point along the load cell.
The present invention has an elevated live rail mounted between two fixed, elevated approach rails. The invention has the advantage of simple installation even though there is a misalignment of the approach rails. Each end of the live rail is supported by a load cell which extends transverse to the live rail. Each load cell is supported by a respective approach rail. Each load cell includes a gauge block and a circular mounting shaft which extends axially from the gauge block and transverse to the live rail. The mounting shaft is inserted into a hole in the live rail. The holes in each end of the live rail are not the same shape. One of the holes is circular in shape and accepts the circular mounting shaft of one of the load cells. The other hole has an oval shape. Specifically, the other hole is elongated in the direction that the rail extends. Thus, some relative translational movement in the direction of the extent of the live rail can occur between the mounting shaft and the live rail.
Specifically, the oval mounting hole allows the live rail to expand or contract under varying temperatures without side loading the mounting shaft. The imposition of side loads upon the mounting shaft can adversely affect the accuracy of a weight measurement. The oval mounting hole also allows for the installation of the live rail between the approach rails without side loading the load cell even though the distance between the ends of the approach rails and thus the load cells may vary from one installation to another. The oval shaped mounting hole in the live rail can tolerate considerable variance in the distance between the mounting shafts of the load cell.
Also the live rail can pivot about the horizontal axis of the mounting shaft of each load cell. Thus, if there is a vertical misalignment of the approach rails, this vertical misalignment can readily be compensated for due to the fact that the live rail can pivot relative to the load cells at its opposite ends.
Also in accordance with the present invention, if the approach rails are laterally misaligned, the construction of the present invention enables the live rail to be mounted therebetween without changing the location at which the load is applied to the load cell. Moreover, if the load hung from the track scale has a center of gravity offset from the longitudinal axis of the rail, as often is the case, the trolley may tilt or cock the rail about a vertical axis. Thus, the live rail twists which could cause the load to be applied to the load cells at a different axial location along the load cell. However, in accordance with the present invention the load force is still applied to the load cell at the same axial location even if such twisting occurs.
The above advantages are achieved by supporting the live rail by respective bearing assemblies which encircle each mounting shaft and are located in the respective mounting holes in the live rail. The bearing assemblies allow tilting or twisting of the live rail and yet the load applied to the mounting shaft of the load cell still remains perpendicular to the mounting shaft axis and is always at the same axial position along the load cell. Also, the bearing assemblies allow the live rail to pivot about the horizontal axis of the mounting shafts. Further, they allow the approach rails at one end of the live rail to be laterally offset relative to the approach rail at the other end.